1. Field of the Invention
The present invention relates to handheld type four-cycle engines, which are mainly used as a power source for machines for portable operation such as trimmers. More particularly, it relates to improvement of an engine head cover structure in which a head cover is joined to the upper end of a cylinder head so as to define a valve operation chamber between the cylinder head and the head cover, and in the head cover are provided an oil recovery chamber which recovers by suction oil resided in the valve operation chamber, and a breather chamber which removes blowby gas from the valve operation chamber.
2. Description of the Prior Art
Such an engine head cover structure is already known as disclosed in, for example, Japanese Patent Application Laid-open No. 11-125107.
In the engine head cover structure disclosed in the above-mentioned publication, the roof of the head cover is split into upper and lower walls so as to define an oil recovery chamber therebetween, and a breather chamber is defined between a partition plate mounted on an inner wall of the head cover and a surface of the roof of the head cover.
Such an arrangement in which the roof of the head cover is split in order to provide an oil recovery chamber requires an oil-tight joint around the whole periphery of the split roof in order to prevent oil leakage from the oil recovery chamber to the outside of the head cover. It is therefore necessary to inspect the joint for oil-tightness, which is a barrier to reducing the production cost.
The present invention has been carried out in view of the abovementioned circumstances, and it is an object of the present invention to provide an engine head cover structure that allows an oil recovery chamber and a breather chamber to be formed without splitting the roof of the head cover and makes inspecting the joint for oil tightness unnecessary thus contributing to a reduction in the production cost.
In accordance with a first characteristic of the present invention, in order to achieve the above-mentioned object, there is proposed an engine head cover structure having a head cover joined to the upper end of a cylinder head so as to define a valve operation chamber therebetween, an oil recovery chamber to which oil resided in the valve operation chamber is recovered by suction and a breather chamber that removes blowby gas from the valve operation chamber, wherein the breather chamber is defined between a partition plate mounted on an inner wall of the head cover and a surface of the roof of the head cover, and the oil recovery chamber is formed integrally with the partition plate.
The above-mentioned valve operation chamber corresponds to a second valve operation chamber 21b of an embodiment of the present invention described below.
In accordance with the above-mentioned first characteristic, the oil recovery chamber and the breather chamber can be provided in the head cover without splitting the roof of the head cover, and moreover, both the breather chamber and the oil recovery chamber can be arranged within the head cover. As a result, even if there is some oil leakage from the two chambers, the oil merely returns to the valve operation chamber and does not cause any problem. It is unnecessary to inspect the peripheries of the two chambers for oil tightness, and it is thus possible to reduce the production cost.
Furthermore, in accordance with a second characteristic of the present invention, in addition to the above-mentioned first characteristic, there is proposed an engine head cover structure wherein the oil recovery chamber is defined between the surface of one side of the partition plate and a partition body welded thereto.
In accordance with the second characteristic, the partition body can be welded to the partition plate prior to mounting the partition plate on the head cover, and it is therefore possible to easily form the oil recovery chamber using the partition plate.
Furthermore, in accordance with a third characteristic of the present invention, in addition to the above-mentioned second characteristic, there is proposed an engine head cover structure wherein a first oil draw-up pipe that opens in the vicinity of the base of the valve operation chamber while communicating with the oil recovery chamber is formed integrally with one of the partition plate and the partition body, and a second oil draw-up pipe that opens in the vicinity of the roof of the head cover while communicating with the oil recovery chamber is formed integrally with the other one of the partition plate and the partition body.
In accordance with the above-mentioned third characteristic, the oil resided in the valve operation chamber can be recovered to the oil recovery chamber by means of the first and second oil draw-up pipes regardless of whether the operational position of the engine is upright or upside down. Moreover, since the first and second oil draw-up pipes are individually formed with one or the other of the partition plate and the partition body, the first and second oil draw-up pipes can be formed easily.
The above-mentioned objects, other objects, characteristics and advantages of the present invention will become apparent from an explanation of a preferable embodiment which will be described in detail below by reference to the appended drawings.